v2 new feature - Trench

As shown on graphic, the Outflow Control options for an Exfiltration
Trench now include a pipe. This is similar to the new option described
in the Pond command.

This is
particularly important if the Trench design is of the Etobicoke
(Toronto) type in which bypass of the trench occurs through a minor
system storm drain passing through the clear stone fill of the trench.